1. Field of the Invention
The present invention relates to new 2,3-bis(hydroxymethyl)-4H-benzo[d]pyrrolo-[1,2-alpha]thiazoles and 1,2-bis(hydroxymethyl)indolizino[6,7-beta]indole derivatives and their bis(alkylcarbamates) derivatives. These derivatives were designed as bi-functional DNA cross-linking agents, and exhibit significant anti-proliferative activity in inhibiting various cancers including human lymphoblastic leukemia, various solid tumor cell growth, human breast carcinoma, and lung cancer.
2. Description of the Related Art
DNA bifunctional alkylating agents, such as thioimidazoles (i.e., carmethizole, 1, FIG. 1),1 bis(hydroxymethyl)pyrrolidine derivatives (i.e., 22 and 33) and 2,3-dihydroxy-6,7-bis(hydroxylmethyl)pyrrolizines [e.g., 4 (IPP)],4 were developed originally from the pyrrolizine alkaloid (5). These agents are able to induce DNA interstrand or intrastrand cross-linking by a mechanism similar to that of mitomycin C derivatives (6, MMCs).3 Unlike MMCs, the DNA cross-linking induced by pyrrolizines does not require the reductive reactivation by reductase. The plausible mechanism of action for DNA interstrand or intrastrand cross-linking induced by bis(carbamoyloxymethyl)pyrroles or pyrrolizines is probably via a SN1 electrophilic reaction.3 Thus, the potential electrophilic reactivity of these agents (the hydroxyl groups or carbamoyl moieties are leaving group in an alkyl-oxygen cleavage mechanism) would be modulated by the degree of electronic perturbation in participating of the pyrrole. Structure-activity relationship (SAR) studies demonstrated that the lipophilicity, planarity, size and the electron properties of the substituent(s) on the C-atom adjunct to the heterocyclic N-atom may also affect their antitumor activity.5 Of bis(hydroxymethyl)pyrrolidine analogues, compound 10 was found to have significant antitumor activity against a broad range of experimental human tumor xenografts.6 phenylpyrrolizines may also affect their antitumor activity.5 Anderson et al. further synthesized bis(carbamoylmethyl) derivatives of pyrrolo[2,1-a]isoquinoline (13 and 14, FIG. 2), which bear angular tricyclic structures to limit the deviation from co-planarity of the phenyl and pyrrolo rings.5 The results showed that these agents exhibited a broad spectrum of antitumor activity against a wide range of tumors.
In our study of bifunctional alkylating agents as potential antitumor agents, we have recently synthesized a series of bis(hydroxymethyl)-8H-3a-azacyclopenta-[α]indene-1-yl and their bis(methylcarbamate) derivatives, which can considered as “benzologue” derivatives of pyrrolizines (4).7 We reported that these agents exhibited significant cytotoxicity in inhibiting human lymphoblastic leukemia and a variety of human tumor cell growth in vitro and have potent therapeutic efficacy in tumor xenograft model. Among these agents, complete tumor remission (CR) in nude mice bearing human breast carcinoma MX-1 xenograft was observed when mice were treated with bis(hydroxymethyl) derivatives, BO-1090 (7, FIG. 2) and BO-1099 (8). Moreover, more than 95% of tumor suppression was achieved when mice bearing human prostate aderonamacarcinoma PC3 xenograft were treated with the bis(methylcarbamates) derivatives, BO-1012 (9) and BO-1124 (10). Remarkably, we found that the combination treatment of BO-1012 (9) with arsenic trioxide (ATO, DNA repair inhibitor) resulted in more than 82% tumor suppression in nude mice bearing human large cell lung carcinoma H460 xenograft and cisplatin-resistant NTUB 1/P human bladder carcinoma xenografts (>92% suppression) in xenograft model.8 More recently, we have synthesized a series of linear 5,10-dihydropyrrolo[1,2-b]isoquinolines and their bis(alkylcarbamates). Of these derivatives, BO-1107 (11) was shown to have potent antitumor activity against human breast carcinoma MX-1 and ovarian adenocarcinoma SK-OV-3 xenografts.9 
Earlier report on the study of the mechanism of action of thioimidazoles (e.g. 1, FIG. 1) or dihydropyrrolo[2,1-b]thiazole (12, FIG. 2)10 suggested that the sulfur atom participates in the expulsion of the hydroxyl or carbamate moiety leading to the nucleophilic attack by DNA.11 Utilizing the known benzo[d]pyrrolo[1,2-a]thiazole diesters,12,13 one can prepare 2,3-bis(hydroxymethyl)-4H-benzo[d]pyrrolo[1,2-a]thiazoles and their bis(alkylcarbamate) derivatives (13), which can be considered as a “benzologue” of compound 12 for antitumor evaluation. A plausible mechanism of action for DNA cross-linking induced by compound 13 is proposed in Scheme 1 as shown in FIG. 3.
Additionally, it was reported that the naturally occurring β-carboline alkaloids and the synthetic indole alkaloids, which possess a common tricyclic 9H-pyrido[3,4-b]indole ring system, also possess potent antitumor activities.14,15 This suggested that β-carboline alkaloids are able to intercalate into the double strands of DNA. Consequently, it is of great interest to apply the tricyclic 9H-pyrido[3,4-b]indole ring system for constructing the new bi-functional DNA alkylating agents, namely 1,2-bis(hydroxymethyl)indolizino[6,7-b]indole derivatives (14, FIG. 2).